The use of RFID technology continues to proliferate as the price-point of RFID transponders and interrogation systems decreases and the need for tracking technology increases. Currently, there are several different types of RF tags, which are usually classified by their power source. Generally, the three major types of RFID tags are purely passive, assisted passive, and active tags.
Purely passive tags have no battery or other type of internal or on-board power source to assist communications. All of its signaling circuitry must be driven using received signal power. Since received signal power is generally on the order of microwatts (μW), or less, a purely passive tag is especially difficult to interrogate over large distances. Because they have no internal power source subject to discharge, purely passive tags generally have an infinite theoretical lifetime of operation.
Assisted passive tags generally require much less power for communications than active tags. An assisted passive tag does not contain active RF components, but does use a small, low-energy power source to drive modulation circuitry. The most common form of assistance is generally from a small watch battery. An exemplary utilization of these RF tags are wireless toll collections on highways. Generally, assisted passive tags have a usable lifetime of 2-3 years.
Active tags use a battery or other on-board power source to drive radio frequency amplifiers as well as baseband and modulation circuitry. The usable range of active tags is generally much larger than a passive tag, although the lifetime of operation is significantly shortened without replenishment of the power supply.
The trade-off between the different types of tags is lifetime vs. range. The truly passive tag should have the lowest reliable range, but the longest usable lifetime. An active tag, on the other hand, could have quite a large range but may only operate for several weeks due to a continuous draw on its on-board battery. Generally, the active tag is usually bulkier and more expensive than the purely passive tag.
It is to be appreciated that all types of RF tags are distinguished from radio beacons, which are transmitters that are always “on” and require no interrogation to extract their information. In contrast to beacons, RF tags are meant for long-lasting, low-powered information exchange.
In many instances, RF tags are bulky and inflexible and have difficulty conforming to surfaces that are not flat. In some instances, they may block a line of sight or prevent the viewing of information or details that lie underneath the RF tag. What is needed are RF tags that overcame challenges found in the art, some of which are described above.